Shield for radio amplifiers or detectors



Oct. 23 1928. 1,688,622

M. E. JOHNSON SHIELD FOR RADIO AMPLIFIERS OR DETECTORS Filed July 8, 1926 INVENTOR P1. E.JOHN5ON WW1- PM ATTORNEY Patented a. 23, 1928.

UNITED. STATES PATENT- OFFICE.

MEBRIAM E. JOHNSON, OF ROCHESTER, NEW YORK, ASSIGNOR THE STROMBERG- OARLSON TELEPHONE MANUFACTURING COMPANY, OF ROCHESTER, NEW YORK, A

CORPORATION OF NEW YORK.

SHIELD FOR RADIO AMPLIFIERS OR DETECTORS.

Application filed. July 8, 1926. Serial No. 121,144.

This invention relates to a shield for a radio detector or amplifier tube and associated equipment.

One object of this invention is to provide'a shield of proper size and shape to enclose a vacuum tube andits related apparatus, such as the tuning condenser, radio frequency transformers,etc.

Another object of this invention is the provision of a metal capwhich fitsinto the top of the shield over the vacuum tube and so arranged as to be readily removed for giving acccss to the tube for replacement purposes.

Still another object of this invention is to construct the shield of metal such as copper of such strength and thickness as to protect the associated apparatus from mechanical inthe metal can showing by means of cross lines,

jury and at the same time reduce the electrical resistance of the shield to strays, etc., thus preventing leakage into the shielded portions of the circuit.

A'further object of this invention is the provision of dampening material such as felt attached to the inner portion of the shield and to the spring fingers of the cap for the purpose of preventing mechanical or acoustic vibrations reaching the tube elements and thus causing acoustic coupling or singing.

In the operation of high efliciency radio reeeivers such as the tuned radio frequency type it has been found very desirable to shield each tuned stage against the e ect of strays, atmospherics a d even signals and in accordance with this invention a heavy copper can with a removable cap is provided asshown in the figures of the accompanying drawmg.

It has also been found very desirable in high efficiency radio receivers,- especially when operating them with cone type loud speakers, to line the copper can or shield with some material which absorbs vibrations in the air and in the structure of the receiver. 'Ilhese vibrations if allowed to reach the vacuum tube, affect the tube electrodes to such an extent, particularly in connection with the detector, as to cause acoustic coupling which interferes with the reception of the desired sig's 'nals. In accordance with this invention the copper can and'cap. are lined with felt.

It has also been found that the vibrations set up by a high quality loud speaker will sometimes cause the system to'go into audio gers which are attached to the inner portion of the cap and these padded fingers grip the tube, thus serving as additional means for preventing vibration of the tube elements.

Referring to the accompanying drawing,

' Fig. 1 is a perspective view of the complete metal can or shield together with its associated metal cap.

Fig. 2 is a perspective view of the inside of the felt lining above referred to.

'Fig. 3 is a perspective view of the inside of the metal cap showing the four spring fingers of this cap and by means of the cross lines, the felt strips attached to these fingers.

Fig. 4 is a horizontal sectional view which shows more clearly the means .of attaching the spring fingers to the cap and in this figure the cross lines represent the metal portion of the cap and fingers, while the heavy black lines represent the felt material.

In the particular form of this inventiondisclosed in the drawings, the can 1 isconstructed or heavy gauge copper, all seams being thoroughly soldered together for the purpose of reducing to a minimum the electricalresistance-of this can to strays, etc. The metal cap 2 is formed of heavy gauge copper,

the thickness .being similar to that used for the can proper. At the open end of cap 2,

portions 3 and 4 are cut out in order to cause this lower portion to act as a spring member for enablingtli'e cap to be readily inserted in or removed frormthe top of the can and at the same time make a good electrical contact. Spring members 5 and 6 are attached to the top central portion of the cap by means of a rivet-7 and these fingers have strips of felt 8, 9, 10 and I1 glued or cemented to their inner portions and are for the purpose of engaging or gripping the vacuum tube over which the cap 2 fits.

A ridge or ring 12 is formed around the lower portion of the cap and acts as a stop for gauging the proper location of this cap within the can top. This distance is so aralso ranged that the felt washer 13 which is glued in the top of the cap rests on the top portion of the vacuum tube. v

The can is formed with over-turned portions lt and 15, which are for attaching the can to the frame or structure of the radio receiver and the holes shown in these portions ,are for the use of screws or rivets for thoroughly fastening the can to the frame.

As shown in Fig. 2 strips of felt 16, 17, 18,

19 (and another strip which is on the inner side of the top portion of this figure and which is not shown) are used for dampening purposes as above mentioned.

A hole 20 is drilled in the top 'of the can and is for the purpose of operating a switch, whichlin some cases may be used for switching different circuit connections of the radio receiver. Another hole 21 is placed in the top of the can and is used for the purpose of inserting a screw driver or other tool for making adjustments of the apparatus 10- dated inside the can. a

Hole 22 drilled in one end of the can is also for use as a means for-inserting an adjusting tool to make adjustments of certain parts of the apparatus.

Portions 23 and 24 are removed from the material forming the sides of the can and are for the purpose of inserting a condenser shaft which operates the condenser associated with lower side and is used to bring the electrical connections from the apparatus located inside the can out to the other portions of the circuit.

- 28 and 29 represent portions of the can which are punchedor cutout in theform of flanges, and are used to clamp or bind the can to an up-turned portion of the frame, these flanges being also used to make a better connection, both mechanically and electrically with the framework of the radio receiver.

By means of the instrumentalitiesdisclosed herewith, I am able to very materially reduce the effect of audio frequenc vibrations, which ordinarily tend to inter ere with the proper operation of the circuit. I am also able to markedly reduce the effect of high frequency currents such as interfering signals and static, ordinarily picked up by the transformer coils and condensers of a radio receiver.

Having now particularly described the nature of my invention and in what manner it may be used, I claim:

1. A shield for a vacuum tube and its associated apparatus, comprising .a metal can for covering said vacuum tube and associated apparatus, a removable cap for said can, and y a vibration insulating lining for said can.

2. A shield for a vacuum tube and its associated apparatus, comprising a metal can lined with vibration absorbing material, and 

